The demand for high quality and high information content LCD and OLED display has been causing a switch from passive to active matrix panels. Both α-Si and poly-Si TFT are used in the construction of active-matrix panels. α-Si TFT technology is simple and mature, but poly-Si TFT can form higher quality display and integrated driver circuit and matrix together. Most companies that manufacture flat panel displays use α-Si TFT technology currently. But poly-Si TFT can be used to improve the quality of the display and can be an important technology for the future.
Manufacturing a conventional α-Si TFT active matrix display panel includes forming gate bus lines and gate electrodes on a substrate; forming a gate insulating layer on the substrate; forming a semiconductor layer on the gate insulating layer; and forming an ohmic contact layer on the semiconductor layer. Also, source bus lines, source electrodes, drain electrodes and electrodes of storage capacitors are formed on the ohmic contact layer. A first passivation layer covers the storage capacitors, the drain electrodes, the semiconductor layer, the source bus lines and the source electrodes; and a second passivation layer covers the first passivation layer and the substrate. Contact holes formed in the first and second passivation layers expose the drain electrodes and the storage capacitors. Pixel electrodes are formed on the storage electrodes, the drain electrodes, the passivation layer, and the substrate. Manufacturing cost of an active-matrix panel is directly proportional to the number of masking steps required. Hence, it is desirable to reduce the number of steps involved in manufacturing these panels.
The present invention provides a much simpler fabrication process of poly-Si TFT active matrix panel for AMLCD and AMOLED, a 30-40% reduction in mask-count is possible, even when compared to that required for the production of α-Si active matrix panels (no driving circuit) used in AMLCD and AMOLED displays.
U.S. Pat. No. 6,025,605 proposes one method to reduce mask process by patterning the second metal layer and impurity-doped semiconductor layer and undoped semiconductor layer in the same step, while source and drain regions are formed in a single processing step, without any additional mask steps.
U.S. Pat. No. 6,365,916 proposes to form the color filters on the active substrate so that the filters also overlap the address lines and function as an insulating layer between the pixel electrodes and address lines in the areas of overlap. Accordingly, the patentee asserts that line-pixel capacitances are reduced and the resulting AMLCD is easier to manufacture. The total number of process step in manufacturing is reduced.
U.S. Published Patent Application No. US2005/023707 proposes aluminum-silicon substitution method to fabricate BJTs with low contact resistance. The method is also applied to form metal plug and metal wiring to reduce resistance, according to JP2004172179. There is no report on its application to parasitic resistance reduction to TFTs and 2-level interconnects formation with one metal layer. The references, patents and patent applications cited herein are incorporated by reference.